Advice please - parasite, salt & sumi

I lost a Bekko last week. I gave it a salt dip at 3 % concentration for a couple of minutes. Not quite sure how long, as I was watching the kois and returning them to the pond one by one - but the Aka Bekko didn't show any signs of stress until it was released back to the pond After half an hour or so it was gone. I had tried holding it over the airstone, but the stress was to severe. It was a doitsu Bekko, should have known it wasn't as strong as the other ones. But as you can see of the pictures it didn't have a very good body, but nice spots though The pictures of the gill it seems there's been some parasites activity in them, and maybe it couldn't get enough oxygen

The reason why I gave all my 8 klois a salt dip was that they all were flashing some now and then. I've had them in a 7 degree pond all winter, so I figured it lightly was Costia causing the flashes . I also raised the temperature between 26 - 28 °C (peaked at 28,4 °C) for about 4 days (outside temp. kept me from raising it further), as I've read that 28 °C will kill Costia. But my problem is of course that I can't be 100 % sure it's Costia. It may also be Trichodina, but I figured that Trichodina isn't that a big threat to healthy koi as Costia..?

Water conditions are good. None detectable nitrite and a working bio filtration system, so likely the Ammonia isn't any problem. Also very little foam formation. Water is very soft. I do not use any salt in my pond, don't believe in salting my kois in the long run.

I also lost a fish during early spring. It had been kind of flashing some all summer last year, but I thought some parasites are normal in a bio pond. In early spring it hid a lot under a rock, acting very unusual. Then I realized it hat scraped it's back and gotten fungus infection. Then I realized that my "leave them be, stability will cure them"-attitude wasn't gonna save him, so I took him in and gave him a treatment of Formalin and Malachite Green. But it only survived two-three weeks. No surprise there really.

After this a younger koi also got signs of wounds in the tail region, and the fish was covered with a grayish layer (not fungus, more like a tone to the skin). So I figured MG & Formalin wouldn't help it much either, so I gave a 2 % salt dip. It seemed to do the trick. And it also got a dip with the rest of the bunch about a week later, and another one 3 days later (2%). This fish is doing better I guess. Wound seems to be healing. (But the sumi is almost gone (it's 2-3 years), and the sumi on my 2 yo Showas is also faded alot! I guess it's due to the high water temperatures I've had the last week. But the odd thing was that the sumi almost went out like a light bulb on the young koi after the last salt dip. )

So my questions:
-Am I right in assuming it was Costia? My first ill koi got sick during a cold water period. The gray layer could also point to Trichodina, but wouldn't all the kois get infected at once with Trichodina?
-If it was Costia, am I likely free of it? Or should I do a PP-treatment and kill all good algea, bacteria, and set the whole pond back to start?
-Do I need to buy an expensive microscope and learn the business of scraping? (Gilll scraping seems like a hassle...)
-Some parasites like Trichodina isn't any problem in small amounts, so as long as water conditions are good, they likely won't cause any issues?

I'm pretty new in the koi buis. Had the pond for a year now. So I'm still eager to learn.

I lost a Bekko last week. I gave it a salt dip at 3 % concentration for a couple of minutes. Not quite sure how long, as I was watching the kois and returning them to the pond one by one - but the Aka Bekko didn't show any signs of stress until it was released back to the pond After half an hour or so it was gone. I had tried holding it over the airstone, but the stress was to severe. It was a doitsu Bekko, should have known it wasn't as strong as the other ones. But as you can see of the pictures it didn't have a very good body, but nice spots though The pictures of the gill it seems there's been some parasites activity in them, and maybe it couldn't get enough oxygen

Poster, I feel you pain! I have seen this MANY times before. The first thing you need to know is that salt at bath concentration can kill koi. The second thing you need to know is that koi infested with costia, chilodonella and trichodina can DEFINITELY be killed by a concentrated salt dip! The gills, when infected are disfunction to a great degree and the salt causes even more irritation and mucous and the fish dies from lack of oxygen/gas exchange.

Next: dipping koi one by one and putting them back into the pond accomplishes one thing-- it weakens your koi and increases the parasite infestation. That is because parasites live ON the koi but swim or are picked up back and forth amongst the school. So each time you dip a koi you strip that koi of its slime coat and take off a large percentage of the parasites. But then you put them back into the pond and they are 'sitting ducks' for instant re-infestation ( from the other koi and the environment) and this time with NO SLIME COAT to protect them! So they all wind up with massive new infestations ( in hours) as the weak, slimless koi are overwhelmed with parasites that now take full advantage and reproduce like mad on fish with no resistance.

The reason why I gave all my 8 klois a salt dip was that they all were flashing some now and then. I've had them in a 7 degree pond all winter, so I figured it lightly was Costia causing the flashes . I also raised the temperature between 26 - 28 °C (peaked at 28,4 °C) for about 4 days (outside temp. kept me from raising it further), as I've read that 28 °C will kill Costia. But my problem is of course that I can't be 100 % sure it's Costia. It may also be Trichodina, but I figured that Trichodina isn't that a big threat to healthy koi as Costia..?

Water conditions are good. None detectable nitrite and a working bio filtration system, so likely the Ammonia isn't any problem. Also very little foam formation. Water is very soft. I do not use any salt in my pond, don't believe in salting my kois in the long run.

I also lost a fish during early spring. It had been kind of flashing some all summer last year, but I thought some parasites are normal in a bio pond. In early spring it hid a lot under a rock, acting very unusual. Then I realized it hat scraped it's back and gotten fungus infection. Then I realized that my "leave them be, stability will cure them"-attitude wasn't gonna save him, so I took him in and gave him a treatment of Formalin and Malachite Green. But it only survived two-three weeks. No surprise there really. No question you need to get on top of this as you will never get rid of the parasites until you;1) stop and investigate2) get a microscope and se what is exactly going on3) review water quality ( tests) and stocking issues4) treat and then quarantine all new purchases.

After this a younger koi also got signs of wounds in the tail region, and the fish was covered with a grayish layer (not fungus, more like a tone to the skin). So I figured MG & Formalin wouldn't help it much either, so I gave a 2 % salt dip. It seemed to do the trick. And it also got a dip with the rest of the bunch about a week later, and another one 3 days later (2%). This fish is doing better I guess. Wound seems to be healing. (But the sumi is almost gone (it's 2-3 years), and the sumi on my 2 yo Showas is also faded alot! I guess it's due to the high water temperatures I've had the last week. But the odd thing was that the sumi almost went out like a light bulb on the young koi after the last salt dip. )You need to stop, take a breath and do the slime coat scaping and do a microscopic exam. I recommend PP for trichodina, costia and chilodonella.

So my questions:
-Am I right in assuming it was Costia?You are wrong-- NEVER assume. It more than 70% of the time leads us down the wrong path to 'guess'. Do the exam

My first ill koi got sick during a cold water period. The gray layer could also point to Trichodina, but wouldn't all the kois get infected at once with Trichodina? I suspect you have a low level of infestation-- it could be multiple species that are hitting your fish at this point. NO ONE can guess which ones they are. IF you have gill flukes most of the reatments you are using are worthless. So again-- get the fish scoped and find out what they have exactly and then us exactly the right chemotherapy

-If it was Costia, am I likely free of it? Or should I do a PP-treatment and kill all good algea, bacteria, and set the whole pond back to start?
-Do I need to buy an expensive microscope and learn the business of scraping? (Gilll scraping seems like a hassle...)
-Some parasites like Trichodina isn't any problem in small amounts, so as long as water conditions are good, they likely won't cause any issues?STOP! you're killing these koi as much as the bigs are. No more treatment! I have visited literally a 100 ponds helping with parasite problems over the years. EVERY pond owner tells me there water quality is perfect and thet can't understand why the fish are dying. Often they tell me then that the water is crystal clear and they test for pH and it is perfect. Or they have plants for a filter or they have 8 fish in 200 gallons of water. There is ALWAYS a reason for a parasite infestation. It is not always environment but often environment is a contributor. So do all the tests ( ammonia, nitrAte, pH etc) and talk with a ZNA chapter member regarding how you do water changes, what the turn over in your filters is, what your filters are like. Feed your koi as you usually do in front of that person. Give a history and sit and discuss the details of when you bought the koi. Let the person watch your koi and the system for a few minutes. An answer will emerge.

I'm pretty new in the koi buis. Had the pond for a year now. So I'm still eager to learn.

Good for you. You ARE learning -- its called the school of hard knocks. Many of the things you are doing now will teach you not to do the same in the future. Don't get frustrated as this learning curve is stressful and often we learn as much from our failures as our success. You will be much wiser after this episode is over. And it will be over once you get on top of what species of parasite you are dealing with. Very best of luck and feel free to ask aditional questions. JR